package com.hducms.common.util;

import java.io.ByteArrayOutputStream;  
import java.io.IOException;  
import java.io.OutputStream;  



public class Base64 {  
	private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();  
	/** 
	 * data[]进行Base64编码转成字符 
	 * @param data 
	 * @return 
	 */  
	public static String encode(byte[] data) {  
		int start = 0;  
		int len = data.length;  
		StringBuffer buf = new StringBuffer(data.length * 3 / 2);  

		int end = len - 3;  
		int i = start;  
		int n = 0;  

		while (i <= end) {  
			int d = ((((int) data[i]) & 0x0ff) << 16)  
					| ((((int) data[i + 1]) & 0x0ff) << 8)  
					| (((int) data[i + 2]) & 0x0ff);  

			buf.append(legalChars[(d >> 18) & 63]);  
			buf.append(legalChars[(d >> 12) & 63]);  
			buf.append(legalChars[(d >> 6) & 63]);  
			buf.append(legalChars[d & 63]);  

			i += 3;  

			if (n++ >= 14) {  
				n = 0;  
				buf.append(" ");  
			}  
		}  

		if (i == start + len - 2) {  
			int d = ((((int) data[i]) & 0x0ff) << 16)  
					| ((((int) data[i + 1]) & 255) << 8);  

			buf.append(legalChars[(d >> 18) & 63]);  
			buf.append(legalChars[(d >> 12) & 63]);  
			buf.append(legalChars[(d >> 6) & 63]);  
			buf.append("=");  
		} else if (i == start + len - 1) {  
			int d = (((int) data[i]) & 0x0ff) << 16;  

			buf.append(legalChars[(d >> 18) & 63]);  
			buf.append(legalChars[(d >> 12) & 63]);  
			buf.append("==");  
		}  

		return buf.toString();  
	}  

	private static int decode(char c) {  
		if (c >= 'A' && c <= 'Z')  
			return ((int) c) - 65;  
		else if (c >= 'a' && c <= 'z')  
			return ((int) c) - 97 + 26;  
		else if (c >= '0' && c <= '9')  
			return ((int) c) - 48 + 26 + 26;  
		else  
			switch (c) {  
			case '+':  
				return 62;  
			case '/':  
				return 63;  
			case '=':  
				return 0;  
			default:  
				throw new RuntimeException("unexpected code: " + c);  
			}  
	}  

	/** 
	 * Decodes the given Base64 encoded String to a new byte array. The byte 
	 * array holding the decoded data is returned. 
	 */  

	public static byte[] decode(String s) {  

		ByteArrayOutputStream bos = new ByteArrayOutputStream();  
		try {  
			decode(s, bos);  
		} catch (IOException e) {  
			throw new RuntimeException();  
		}  
		byte[] decodedBytes = bos.toByteArray();  
		try {  
			bos.close();  
			bos = null;  
		} catch (IOException ex) {  
			System.err.println("Error while decoding BASE64: " + ex.toString());  
		}  
		return decodedBytes;  
	}  

	private static void decode(String s, OutputStream os) throws IOException {  
		int i = 0;  

		int len = s.length();  

		while (true) {  
			while (i < len && s.charAt(i) <= ' ')  
				i++;  

			if (i == len)  
				break;  

			int tri = (decode(s.charAt(i)) << 18)  
					+ (decode(s.charAt(i + 1)) << 12)  
					+ (decode(s.charAt(i + 2)) << 6)  
					+ (decode(s.charAt(i + 3)));  

			os.write((tri >> 16) & 255);  
			if (s.charAt(i + 2) == '=')  
				break;  
			os.write((tri >> 8) & 255);  
			if (s.charAt(i + 3) == '=')  
				break;  
			os.write(tri & 255);  

			i += 4;  
		}  
	}  

}  
